Plants are known to produce useful compounds such as phytochemicals during metabolic activities. Phytochemicals can be used in pharmaceutical products and health foods. Further, plant metabolism depends on growth environments of the plant. Therefore, the types and amounts of compounds produced in the course of the plant metabolism are thought to be changed by altering environment factors related to the growth of the plant. Accordingly, studies have been traditionally conducted for allowing plants to produce useful compounds such as phytochemicals by changing environmental factors related to the growth of the plants.
As phytochemicals, for example, polyphenol is known. Patent Document 1 discloses a method of manufacturing germinated plant seeds, comprising maintaining plant seeds under atmosphere conditions of a carbon dioxide concentration of 2000 ppm or more and/or an oxygen concentration of 18 vol % or less and further maintaining the plant seeds at a temperature within the range of the germination temperatures, wherein the amount of a readily water-soluble polyphenol is increased.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2008-125515